As used herein, certain terms are defined as follows:
"Polyolefin" means polyethylene, polypropylene, ethylene/propylene copolymer and polyallomer, and such polyolefins containing rubber, such as ethylene/propylene rubber (EPR) modified polypropylene block copolymer.
"Sheets" or "sheet material" includes thin film material as well as heavier sheets.
Copolyesterethers are tough flexible materials and can be extruded into clear sheets. Such sheets are particularly useful in the packaging of intravenous solutions. However, water tends to have a high diffusion rate through these Films and intravenous solutions packaged in these materials lose water from the solution. While the loss from the intravenous solution has been solved by using an outer overwrap or the intravenous solution container, this is undesirable because of expense and having to make two separate bags For each solution.
This invention, in one aspect, provides multilayered clear flexible films which may be formed by coextrusion. These films have excellent water vapor barrier properties and excellent adhesion before and after autoclaving. They have three or more layers and consist of at least one layer each of a flexible copolyesterether, a water vapor barrier layer of a polyolefin and an adhesive or tie layer for bonding the copolyesterether layer to the polyolefin layer. These films can be formed into containers for materials such as intravenous solutions.
By using layers of the copolyesterether, tie layer and polyolefin, films can be constructed with excellent water vapor barrier and adhesion before and after autoclaving. Polyolefins are excellent water vapor barriers, but are rigid. However, thin layers have sufficient flexibility and water barrier properties. Since copolyesterethers and polyolefins in general do not adhere to each other even when brought together in the melt, it is necessary to use an intermediate adhesive or tie layer that will stick to both the copolyesterether and polyolefin layers. The adhesive or tie layer must provide good adhesion before and after autoclaving to prevent delamination in the container.
Patents of interest include U.S. Pat. Nos. 4,643,926; 4,119,267; 4,210,686 and 4,349,469. The '926 patent discloses a flexible film comprising several layers of polymeric material. For example, one of the flexible films disclosed comprises a polyallomer and a flexible copolyester (such as the copolyesterether described herein) tied together with various tie layers (for example, an ethylene propylene copolymer, Column 4, lines 7 and 8). Applicants' examples indicate unexpected improved results in adhesion using the low molecular weight polyethylene with a Flow rate of 0.25 to 40, over the tie layers disclosed by this reference. Furthermore, published technical literature by Mitsui petrochemical Industries, Ltd., directed to Admer resins discloses the utility of low molecular weight polyethylene resins as adhesive layers between various materials including certain plastics. However, we have not found a disclosure or suggestion that these resins are particularly effective as a tie layer between copolyesterether or certain copolyesters and polyolefins as called for herein.
There are, of course, other instances where it may be desirable to bond copolyesterethers, certain copolyesters (or blends thereof) to polyolefins. For example, copolyesterethers or copolyesters may be used as carrier sheets for decorative and/or protective coatings to be applied to polyolefin material.